Thrust chamber milling seam fiber coupling laser-air coupling ultrasonic reflection type detection system and method

Abstract

The application discloses a kind of thrust chamber milling groove weld fiber coupling laser-air coupling ultrasonic reflection type detection system and method, the system includes high-frequency pulse laser, fiber coupling laser focusing lens, focusing air coupling ultrasonic transducer, control computer equipped with ultrasonic signal acquisition and processing software, scanning motion mechanism.The detection method is: using fiber coupling pulse laser in the inner wall of thrust chamber milling groove to carry out ultrashort pulse ultrasonic wave excitation, ultrasonic wave propagates inside milling groove structure, and the leak defect of brazing layer will hinder the propagation of ultrasonic wave, and the ultrasonic signal of focusing air coupling ultrasonic transducer is collected at the position of inner wall, so as to realize the detection of internal brazing defect, and the thrust chamber is scanned quickly by computer control motion scanning mechanism, that is, the overall evaluation of brazing quality of thrust chamber is realized.The application effectively solves the problem that conventional detection method cannot detect milling groove brazing seam, reduces the influence of specimen surface finish on detection result, reduces the cost of detection equipment, and improves the evaluation efficiency of thrust chamber milling groove brazing seam defect.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, specifically to a fiber-coupled laser-air-coupled ultrasonic reflection detection system and method for thrust chamber milled groove welds, which can realize rapid detection and high-resolution imaging of defects in the milled groove brazed welds of liquid rocket engine thrust chambers. Background Technology

[0002] As a critical propulsion system for launch vehicles, the structural safety evaluation of liquid rocket engines is self-evident. To ensure the stability and reliability of liquid rocket engine performance during service, the thrust chamber typically employs a sandwich structure between its inner and outer walls for regenerative cooling. Common sandwich structures include corrugated plate structures and milled groove brazed structures. Due to factors such as manufacturing processes, incomplete penetration, brazing filler metal accumulation, and blockages in the sandwich structures can occur, severely impacting product performance. The quality of the brazed joints in the thrust chamber body is one of the key factors affecting rocket engine safety. Utilizing advanced non-destructive testing technologies for rapid and effective quality inspection is crucial for ensuring engine safety and reliability.

[0003] For the quality inspection of brazed seams in corrugated plate structures, conventional radiographic testing is currently the primary method, supplemented by hydraulic strength testing. However, for the quality inspection of brazed seams in milled groove structures, due to their structural characteristics—the gap after welding is extremely small, only 0.02 mm, and the large height of the milled groove ribs obscuring the brazed seams—conventional radiographic testing methods are unsuitable. Currently, hydraulic strength testing is the main method, lacking effective preventative non-destructive testing techniques. Meanwhile, non-contact ultrasonic testing technologies such as laser ultrasound and air-coupled ultrasound are increasingly developing and maturing, while also facilitating efficient inspection and non-contact evaluation. Therefore, combining the advantages of laser and air-coupled ultrasound, the laser-ultrasonic fiber-optic coupled reflective inspection system and method for thrust chamber milled groove welds provides greater feasibility for the inspection of milled groove brazed structures. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that conventional inspection methods for milled groove brazing welds in the thrust chamber of liquid rocket engines cannot detect them, and to provide a fiber-coupled laser-air-coupled ultrasonic reflection inspection system and method for milled groove brazing welds in the thrust chamber.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milling groove welds includes: a high-frequency pulsed laser 1, an optical fiber 2, a fiber-coupled laser focusing lens 3, a focused air-coupled ultrasonic transducer 4, a preamplifier 7, a bandpass filter 8, an oscilloscope 9, a control computer 10 equipped with signal acquisition and processing software, and a motion scanning mechanism 11. The fiber-coupled laser focusing lens 3 is connected to the high-frequency pulsed laser 1 via the optical fiber 2. The motion scanning control mechanism 11 synchronously controls the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4. After receiving a trigger signal from the high-frequency pulsed laser 1, the oscilloscope 9 begins to acquire the time-domain signal measured by the focused air-coupled ultrasonic transducer 4 after passing through the preamplifier 7 and the bandpass filter 8. The control computer 10, equipped with signal acquisition and processing software, is responsible for acquiring and storing the signal from the oscilloscope 9 and synchronously controlling the motion scanning mechanism 11.

[0007] When inspecting the milled thrust chamber after brazing, the high-frequency pulsed laser 1 emits a Gaussian pulsed laser beam that travels through the optical fiber 2 to the fiber-coupled laser focusing lens 3. The focused pulsed spot irradiates the upper part of the thrust chamber's inner wall ribs, forming ultrasonic waves 5 that propagate along the ribs to the outer wall. The brazing defects 6 inside the thrust chamber reflect the ultrasonic waves and propagate them to the inner wall, thus forming local ultrasonic signal characteristics on the inner wall. The out-of-plane displacement ultrasonic signal of this area is collected non-contactly by the focused air-coupled ultrasonic transducer 4, thereby realizing the detection at this location. The fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are scanned and collected by the motion scanning mechanism 11, thus realizing the detection of the overall brazing quality of the thrust chamber.

[0008] The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds includes the following steps:

[0009] Step 1: Install the fiber-coupled laser-air-coupled ultrasonic reflective detection system for the milled groove weld of the thrust chamber. Use a reflective arrangement for scanning and acquisition, that is, the excitation end and the detection end of the ultrasonic are on the same side. First, tilt the fiber-coupled laser focusing lens 3 and tilt the excitation pulse laser incident to coincide with the air-coupled detection focus point of the focused air-coupled ultrasonic transducer 4. Adjust the scanning and detection position.

[0010] Step 2: Set the scanning length in the x-axis direction to L1, the spacing to Δx, and the number of scanning points to m = L1 ÷ Δx + 1; the scanning length in the y-axis direction to L2, the scanning spacing to Δy, and the number of scanning points to n = L2 ÷ Δy + 1; the total area of ​​the scanning region to L1 × L2; and the total number of scanning points to m × n. Move the test piece back and forth along the scanning region 13 to perform two-dimensional scanning detection.

[0011] Step 3: Obtain the volume wave time domain signal S at each measurement point using two-dimensional scanning. 1,1 (t), S1,2 (t)…S 1,m (t), S 2,1 (t), S 2,2 (t)…S 2,m (t)…S n,1 (t), S n,2 (t)…S n,m (t), which are sequentially arranged to form a two-dimensional signal data matrix S(t,m×n);

[0012] Step 4: Perform bandpass digital filtering on the translated and aligned two-dimensional signal data matrix S′(t,m×n), and then extract the ratio of the peak value at the defect location to the peak value of the bottom echo as the defect feature to obtain the two-dimensional signal matrix A(x,y) corresponding to the ratio and the coordinates of the scanning point.

[0013] Step 5: Take the two-dimensional signal matrix A(x,y) corresponding to the ratio and the coordinates of the scanning point, set the interpolation step size, and obtain the two-dimensional signal matrix V(x,y) after interpolation and normalization;

[0014] Step 6: Perform imaging processing on the two-dimensional signal matrix V(x,y) after interpolation and normalization to obtain defect detection imaging images of the defect location and size of the test piece, namely, one-dimensional B-scan image, synthetic aperture algorithm imaging image, and two-dimensional C-scan image.

[0015] Both the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 mentioned in step 1 are non-contact and adopt a reflective scanning acquisition method. The excitation pulse laser is obliquely incident on a small area above the milled groove rib of the thrust chamber. The size of the laser spot is controlled to be the same as the width of the rib, thereby achieving precise excitation of ultra-short pulse ultrasonic waves. This effectively reduces the interference of reflected signals from the inner wall of the thrust chamber and the rib boundary, while also reducing the blind zone effect on the bottom surface of the outer wall of the thrust chamber. By adjusting the size and shape of the pulse laser spot to excite the small area, higher directivity can be obtained. Pulsed lasers are more suitable for ultrasonic excitation of metal materials with high acoustic impedance, while the focused air-coupled ultrasonic transducer 4 is more suitable for exciting ultrasonic waves in materials with low acoustic impedance. In addition, pulsed lasers generate different waveforms in metal materials. By adding a constraint layer to the surface of the specimen, i.e., coating the surface of the specimen with a transparent liquid film, the heat in the laser irradiation area causes the liquid to evaporate, generating a greater reaction force, thereby enhancing the amplitude of the longitudinal wave signal and changing the directivity of the ultrasonic waves.

[0016] The ratio of the peak value at the defect location to the peak value of the bottom echo, as described in step 4, is a defect feature acquired by a reflective arrangement. If the distance between the focused air-coupled ultrasonic transducer 4 and the surface of the test piece changes, resulting in a partial shift in the time domain signal, the shifted signal will be corrected in the time domain before signal processing.

[0017] The interpolation step size setting mentioned in step 5 is adjusted according to the scanning step size. In order to obtain better interpolation results, the scanning step size is set to one-tenth of the minimum scanning step size, i.e., min(Δx,Δy) / 10.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention addresses the problem that conventional methods for inspecting brazed weld seams in milled grooves are ineffective. It utilizes a fiber-coupled laser-air-coupled ultrasonic testing system and method for rapid scanning and inspection of the brazed weld quality in thrust chamber milled grooves. During the inspection, a defect detection image is generated, showing the location and size of defects. This provides a feasible inspection system and method for inspecting the quality of brazed weld seams in thrust chamber milled grooves. Because the focused air-coupled ultrasonic transducer does not require optical focusing like optical inspection equipment (such as laser interferometers), it only needs to be placed directly above the rib, with the distance between the focused air-coupled ultrasonic transducer and the surface of the test piece controlled to be one focal length. Furthermore, compared to optical inspection equipment, the focused air-coupled ultrasonic transducer is smaller, cheaper, and easier to install and use. Therefore, it reduces the influence of the surface finish of the test piece on the inspection results, lowers the cost of inspection equipment, and achieves rapid non-contact scanning. Through two-dimensional scanning and data post-processing, it further improves the efficiency of inspection and evaluation. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the laser-coupled ultrasonic reflection scanning detection method involved in the present invention;

[0021] Figure 2 This is a flowchart illustrating the specific implementation steps of the present invention;

[0022] Figure 3 This is a schematic diagram of the signal processing process involved in the present invention, wherein (a) is a scanning signal processing process, (b) is a translational alignment scanning signal processing process, and (c) is a schematic diagram of two-dimensional C-scan imaging of the scanning area. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1As shown, this invention discloses a fiber-coupled laser-air-coupled ultrasonic reflection detection system and method for thrust chamber milling groove welds, comprising: a high-frequency pulsed laser 1, an optical fiber 2, a fiber-coupled laser focusing lens 3, a focusing air-coupled ultrasonic transducer 4, a preamplifier 7, a bandpass filter 8, an oscilloscope 9, a control computer 10 equipped with signal acquisition and processing software, and a motion scanning mechanism 11; wherein the fiber-coupled laser focusing lens 3 is connected to the high-frequency pulsed laser 1 via the optical fiber 2, the motion scanning control mechanism 11 synchronously controls the fiber-coupled laser focusing lens 3 and the focusing air-coupled ultrasonic transducer 4, the oscilloscope 9 receives a trigger signal from the high-frequency pulsed laser 1 and begins to acquire the time-domain signal measured by the focusing air-coupled ultrasonic transducer 4 after passing through the preamplifier 7 and the bandpass filter 8, the control computer 10 equipped with signal acquisition and processing software is responsible for acquiring and storing the signal from the oscilloscope 9, and synchronously controlling the motion scanning mechanism 11. When inspecting the milled thrust chamber after brazing, the high-frequency pulsed laser 1 emits a Gaussian pulsed laser beam that travels through the optical fiber 2 to the fiber-coupled laser focusing lens 3. The focused pulsed spot irradiates the area above the inner wall ribs of the thrust chamber 14, generating ultrasonic waves 5 that propagate along the ribs to the outer wall. The brazing defects 6 inside the thrust chamber reflect the ultrasonic waves and propagate them to the inner wall, thus forming local ultrasonic signal characteristics on the inner wall. The out-of-plane displacement ultrasonic signal of this area is collected non-contactly by the focused air-coupled ultrasonic transducer 4, thereby achieving detection at this location. The fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are scanned and collected by the motion scanning mechanism 11, thus achieving the detection of the overall brazing quality of the thrust chamber.

[0025] The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds, the implementation steps are as follows: Figure 2 As shown, the details are as follows:

[0026] Step 1: Install the fiber-coupled laser-air-coupled ultrasonic reflective testing system for the milled groove weld of the thrust chamber. This method adopts a reflective arrangement, that is, the fiber-coupled laser focusing lens 3 and the focused air-coupled ultrasonic transducer 4 are placed on the same side of the test piece. First, the excitation pulse laser is tilted and incident to coincide with the detection focus point of the focused air-coupled ultrasonic transducer, and the scanning and detection position is adjusted.

[0027] Step 2: Set the scanning length in the x-axis direction to L1, the spacing to Δx, and the number of scanning points to m = L1 ÷ Δx + 1; the scanning length in the y-axis direction to L2, the scanning spacing to Δy, and the number of scanning points to n = L2 ÷ Δy + 1; the total area of ​​the scanning region to L1 × L2; and the total number of scanning points to m × n. Move the test piece back and forth along the scanning region 13 to perform two-dimensional scanning detection.

[0028] Step 3: Obtain the volume wave time domain signal S at each measurement point using two-dimensional scanning. 1,1(t), S 1,2 (t)…S 1,m (t), S 2,1 (t), S 2,2 (t)…S 2,m (t)…S n,1 (t), S n,2 (t)…S n,m (t), sequentially forming a two-dimensional signal data matrix S(t,m×n), such as Figure 3 As shown in (a);

[0029] Step 4: As Figure 3 As shown in (b), the two-dimensional signal data matrix S′(t,m×n) that has been translated and aligned is subjected to bandpass digital filtering, and the ratio of the peak value at the defect location to the peak value of the bottom echo is taken as the defect feature, so as to obtain the two-dimensional signal matrix A(x,y) corresponding to the ratio and the coordinates of the scanning point.

[0030] Step 5: Take the two-dimensional signal matrix A(x,y) corresponding to the ratio and the coordinates of the scanning point, set the interpolation step size to one-tenth of the minimum scanning step size, i.e., min(Δx,Δy) / 10, and obtain the two-dimensional signal matrix V(x,y) after interpolation and normalization.

[0031] Step 6: Perform imaging processing on the two-dimensional signal matrix V(x,y) after interpolation and normalization to obtain defect detection imaging images of the test piece, showing the location and size of defects, such as one-dimensional B-scan images, synthetic aperture algorithm imaging images, and two-dimensional C-scan images. Figure 3 (c) is a schematic diagram of the two-dimensional C-scan imaging of the scanned area. The entire area of ​​the image represents the experimental scanned area. Parallel to the y-axis is the location of the milled groove rib. The ribs are cooling channels, and the discontinuities above the ribs are brazing defects.

Claims

1. A detection method for a fiber-coupled laser-air-coupled ultrasonic reflection detection system for milled groove welds in thrust chambers, the detection system comprising: The system includes a high-frequency pulsed laser (1), an optical fiber (2), an optical fiber-coupled laser focusing lens (3), a focused air-coupled ultrasonic transducer (4), a preamplifier (7), a bandpass filter (8), an oscilloscope (9), a control computer (10) equipped with signal acquisition and processing software, and a motion scanning mechanism (11). The optical fiber-coupled laser focusing lens (3) is connected to the high-frequency pulsed laser (1) via the optical fiber (2). The motion scanning mechanism (11) synchronously controls the optical fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4). After receiving the trigger signal from the high-frequency pulsed laser (1), the oscilloscope (9) begins to acquire the time-domain signal measured by the focused air-coupled ultrasonic transducer (4) after passing through the preamplifier (7) and the bandpass filter (8). The control computer (10) equipped with signal acquisition and processing software is responsible for acquiring and storing the signal from the oscilloscope (9) and synchronously controlling the motion scanning mechanism (11). The detection method is characterized by comprising the following steps: Step 1: Install the fiber-coupled laser-air-coupled ultrasonic reflective detection system for the milled groove weld of the thrust chamber. Use a reflective arrangement for scanning and acquisition, i.e., the excitation end and the detection end of the ultrasonic are on the same side. First, place the fiber-coupled laser focusing lens (3) at an angle and make the excitation pulse laser incident at an angle to coincide with the air-coupled detection focus point of the focused air-coupled ultrasonic transducer (4). Adjust the scanning and detection position. Step 2: Set the scan length in the x-axis direction as... The spacing is The number of scan points is The scan length along the y-axis is The scanning interval is The number of scan points is The total area of ​​the scanned region is The total number of points in the scanned area is The test piece is moved back and forth along the scanning area (13) to perform two-dimensional scanning detection; Step 3: Obtain the volume wave time domain signal at each measurement point using two-dimensional scanning. , , , , Sequentially forming a two-dimensional signal data matrix ; Step 4: Align the translated two-dimensional signal data matrix Bandpass digital filtering is performed, and the ratio of the peak value at the defect location to the peak value of the bottom echo is extracted as the defect feature, resulting in a two-dimensional signal matrix corresponding to the ratio and the coordinates of the scan point. ; Step 5: Obtain the two-dimensional signal matrix corresponding to the ratio and the coordinates of the scan points. Set the interpolation step size, and obtain the two-dimensional signal matrix after interpolation and normalization. ; Step 6: Perform interpolation and normalization on the two-dimensional signal matrix. Imaging processing is performed to obtain defect detection imaging images that include the location and size of defects in the test piece, namely, one-dimensional B-scan image, synthetic aperture algorithm imaging image, and two-dimensional C-scan image.

2. The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds according to claim 1, characterized in that: When inspecting the milled thrust chamber after brazing, the high-frequency pulsed laser (1) emits a Gaussian pulsed laser beam that reaches the fiber-coupled laser focusing lens (3) via the optical fiber (2). The focused pulsed spot irradiates the upper part of the inner wall rib of the thrust chamber and forms an ultrasonic wave (5) that propagates along the rib to the outer wall. The brazing defects (6) inside the thrust chamber reflect the ultrasonic wave and propagate to the inner wall, thereby forming local ultrasonic signal characteristics on the inner wall. The out-of-plane displacement ultrasonic signal of the area where the local ultrasonic signal characteristics are located is collected non-contactly by the focused air-coupled ultrasonic transducer (4) to realize the detection at the irradiation position of the spot. The fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4) are scanned and collected by the motion scanning mechanism (11), thus realizing the detection of the overall brazing quality of the thrust chamber.

3. The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds according to claim 1, characterized in that, The fiber-coupled laser focusing lens (3) and the focused air-coupled ultrasonic transducer (4) mentioned in step 1 are both non-contact and adopt a reflective arrangement for scanning and acquisition. The excitation pulse laser is obliquely incident on a small area above the milled groove rib of the thrust chamber. The size of the laser spot is controlled to be the same as the width of the rib, thereby achieving precise excitation of ultra-short pulse ultrasonic waves, effectively reducing the interference of the reflected signals of the inner wall of the thrust chamber and the rib boundary, and reducing the blind zone effect of the bottom surface of the outer wall of the thrust chamber. By adjusting the size and shape of the pulse laser spot, the small area is excited to obtain higher directivity. The pulse laser is more suitable for ultrasonic excitation of metal materials with high acoustic impedance, while the focused air-coupled ultrasonic transducer (4) is more suitable for exciting ultrasonic waves in materials with low acoustic impedance. In addition, the pulse laser generates different waveforms in metal materials. By adding a constraint layer to the surface of the specimen, i.e. coating the surface of the specimen with a transparent liquid film, the heat of the laser irradiation area causes the liquid to evaporate and generate a greater reaction force, thereby enhancing the amplitude of the longitudinal wave signal and changing the directivity of the ultrasonic waves.

4. The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds according to claim 1, characterized in that, The ratio of the peak value at the defect location to the peak value of the bottom echo described in step 4 is a defect feature of the signal acquired by the reflective arrangement. If the distance between the focused air-coupled ultrasonic transducer (4) and the surface of the test piece changes, resulting in a partial offset in the time domain signal, the offset signal should be corrected in the time domain before signal processing.

5. The detection method of the fiber-coupled laser-air-coupled ultrasonic reflection detection system for thrust chamber milled groove welds according to claim 1, characterized in that, The interpolation step size setting described in step 5 is adjusted based on the scanning step size. To obtain better interpolation results, the scanning step size is set to one-tenth of the minimum scanning step size, i.e. .

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